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Can I connect a broadband router to a standard ethernet switch?

Posted on 2002-05-21
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Problem:  I have a DSL connection through a cisco 678, that was connected to a linksys befsr80 cable/dsl router for my LAN.  I had the linksys router setup with the IP of my domain name, and had the http and FTP ports forwarded to an internal computer hosting the web site, using an internal IP - 192.168.1.100.  The subnet mask for the ip associated with my domain name is 255.255.255.248.  The subnet mask for the internal network was- 255.255.255.0.  So I changed the subnet mask on the internal network to ...248.  As soon as I changed the mask on the linksys- I lost the setup screen through http: and havent been able to get it back regardless of the ip, or masks that I use on the network.
   I was just considering buying a 24 port standard ethernet switch, and I cant think of a reason why I cant take the data from the cisco broadband router, and rather than connect it to a computer, as I'm doing right now; connect it to a switch?  If it can be done- what kind of switch, or what features does the switch need to have?  Or does it have to go to a router, and if so... will a standard router do?  What features would it need?
   I need at least 8 ports- and I'm not real interested in Linksys.  there tech support is at best- non-existent, as I've found out, as is information about how to get into that router other than through the http: setup screen.
Any help- much appreciated.
Rick
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Question by:rixxagain
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by:scraig84
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From the sound of your explanation, you have "bridged" DSL service.  In this case you cannot just plug the Ethernet into a switch or hub.  It will need to be a PC or router.  

No offense, but to me it sounds like you are a bit confused on how IP connectivity works.  The fact that you changed your internal subnet mask because "the ip associated with the domain name is 255.255.255.248" is a bit odd.  First off, there is no mask associated with an IP for a domain name.  If that is the mask of the network on which the ip associated with your domain name exists, that would make more sense.  However, there would be absolutely no reason to change the internal ip structure for this.

My assumption from working with Linksys devices that it has the address of 192.168.1.1 and it sounds like you changed the internal mask to 255.255.255.248.  To connect to it, you simply need to address a machine with 192.168.1.2 (last digit can actually be any number between 2 and 6) and give it the same mask.  From there you will be able to connect to the Linksys again and give it the old mask back.  Linksys makes a perfectly good broadband router, and I can guarantee you that no manufacturer is going to document proper IP addressing - so you would have been up a creek with any vendor's product in this situation.  

I would recommend in the future that you make sure you have a full understanding of the IP changes you make so that you can easily recover from them.
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by:Hollmer
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What I do at home is this.

I plug my DSL directly into my Windows 2000 Advanced Server and I NAT all of my internal addresses to my single external IP.  It sounds like what you're trying to do is to have the DSL "router" (which is actually just a bridge to the DSL providers network), drop into another router and let that "router" take care of your NATing.  That will work but it's very tricky to set up.  Changing your Subnet mask to match will not do it.  What you need to do is to put your public IP address on the internal routers external interface and have that router NAT all the addresses for your internal machines.  (confused?)

1.  Signal comes into your DSL router.
2.  Signal drops to your internal interface of same router.
3.  Signal then hits the external interface of the internal router.
4.  Signal is distributed to each machine from THAT router.  Not the DSL router.  

This is the hard way of doing it.  Just get a copy of Windwos 2000 Advanced Server or XP and do it that way.  Setup is MUCH easier.

-Rick
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by:scraig84
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Hollmer - first off he has an additional Linksys device that he had set up for NAT and routing based on the information I read in the original question.  Second, setting up a Cisco 675 or 678 is not at all "tricky" to set up.  It is no "trickier" than any other NAT device out there and has very few extra lines from just setting the thing up to bridge.  Third, now that he already has 2 devices in his environment that can easily perform NAT capabilities, why on Earth would he want to invest in another device and/or OS (assuming nobody illegally uses unlicensed software) for this purpose?

As I noted in my response (and I am pretty certain I am correct), I don't believe that the problem he is having is a lack of understanding of the equipment he is using (although that could play a part), his primary issue is not understanding basic IP functionality and subnet masking.  I do not fault him for this, but at the same time I don't think that alternative solutions need to necessarily be offered when the same underlying issue remains the same.
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by:rixxagain
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Ya know scraig, after reading your post- it just dawned on me what you are likely saying.  On the internal network- none of the pcs' have a network IP between 192.168.1.2 and 192.168.1.6.  So, when I changed the mask- all of them became unavailable to access the setup screen.  How dumb of me.
   Your right though- I am confused about all of this IP/masking thing, and am just starting to tackle it now.
   Question:  I believe the router is a ppp DSL.  Not certain but- if it was- could I use a standard ether switch?
   Also- what exactly is NAT, or how does it work?
Hollmer- when you say that you NAT all your internal machines to your external IP; does that mean that you set all the internal machines default gateway to your external IP?  Also- do you have to run some kind of NAT program like winroute pro?
I wont be in my office for a few hours yet- I'll try this right away.
Many thanks for your help.
Rick

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by:scraig84
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Everything you ever wanted to know about NAT:

http://www.cisco.com/warp/public/556/index.shtml

The short and skinny is that NAT translates internal addresses that don't work on the internet such as 10.x.x.x or 192.168.x.x etc to working IP addresses that are publicly routed.  This allows for greater flexibility within the confines of a private network, while still giving global connectivity.  A device such as a router or a server performs the translation between real (public) and fake or unroutable (internal) addresses.

Your ability to plug the 678 directly into a switch depends on the configuration of the 678 as well as how the ISP handles things.  I am assuming that is what you are asking although I am not entirely clear on your question.  Do you know if the 678 has an IP address of its own on its Ethernet interface?  If so, than you could theoretically plug it in and publicly address your devices.  However, you have a perfectly good broadband router and if I were you, I would concentrate on getting it to work properly for you since it will do the job for you.
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by:rixxagain
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The phone company here, who is my ISP, offers blocks of 8 IP addresses that one can lease, which I did.  Of those 8 IPs'- 5 are useable, and the others are reserved for things like the DSL router.  Its this block of 8 IPs that they said has the subnet of 255.255.255.248.  How the hell that is relevant- I dont know.  The way it is right now- the 678, and the external interface for the linksys operate with a subnet mask of 255.255.255.248.  The internal network, if I ever get into my office to fix it, will operate on a subnet of 255.255.255.0.  This is where this stuff confuses me.  
   On my little office network now:  the 678 may have, for example, the IP address of 67.44.70.236 connected to the internet.  The Linksys router maybe, the IP 67.44.70.234 on the external interface, and 192.168.1.1 on the internal interface, and has ip forwarding to the web server, 192.168.1.100.  
   If the 678 has an IP- can I use a switch?  Does the switch have to be able to be assigned an IP in order to work?  The reason that I ask is this.
   There are only 6 PCs on the network right now.  However- we are presently buying the buiding that we are in, and will be adding at least 8 more.  I'm going to end up buying a switch anyways, and if it will do what the 678 is doing- I can use the 678 at home.  Rather than having to buy both.
   I didnt get a chance yesteday to test the linksys.  I should today.  ( Yea- right ).
  Hope this helps.  Thx again Scraig.
Rick

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scraig84 earned 400 total points
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The mask they gave you is relevant because any device communicating directly with the 678 will need that mask.  Currently that is just the outside interface of the Linksys.  

Yes - you could plug the 678 directly into a switch and you could address your machines to be on the 67.44.70.232 network.  However, you only have 5 usable IP addresses in this scenario and you currently have 6 machines with more on the way.  

My suggestion is for you to keep your Linksys and keep doing translation (NAT).  The reason you are able to have more machines on the inside and consequently use a larger subnet mask is that NAT is translating those internal addresses to the public addresses.  Among other things, this allows multiple internal devices to use a single (or small number of) public IP addresses.

Now, I just reread part of your post and it sounds like you want to REPLACE the 678 with a switch?  No, you can't do that.  The 678 is designed to communicate specifically over a DSL line and move traffic back and forth from DSL to Ethernet.  A normal Ethernet switch will not do that.  I don't know what you would use the 678 at home for, unless it would be for DSL, in which case your provider should give you a modem of some kind.

Hope that helps.
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by:rixxagain
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Yes- that helps alot.  This thread is gettin way off target here huh?
   I guess I'll need NAT here too, huh, for all the PCs.  My primary goal notwithstanding- I'm tryin to setup a web server from my office.  Before I lost the screen on the linksys- I believe it was setup the right way.  However- if I try to browse to it from another outside computer- it says that the page cant be displayed.  It looks like the DNS is working.  If I try and trace route, or ping the linksys- it times out.  If Itry and ping, or tracert the 678- it responds.  I cant tell if its the interface fromn the 678 to the linksys, or if its the linksys, that is stopping the packets.
  A person at the tech support for the phone company said that I have to open a port on the 678 to allow HTTP and FTP requests.  He is the only one that has said that.  Noone else seemed to know what he was talkin about.
   Do you know of any validity in this?  I thought port 80 was, or has, to be open for anything to pass.  
   I was going to use the 678 at home for DSL.  They charge us $300.00plus for them.

Thx again scraig.  I'll up the points on this when its done.  You've been most helpful.

   Are you a member on this site?  I'm thinking about joining. Ya know- $9.00 p/month, or whatever?

See ya scraig
Rick
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by:rixxagain
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I want to assign these points while I have the time Scraig.  Everything you said worked perfectly.  I got the setup screen back on the router- set it up for the web server- Wala-- no probs.
   Many thanks for the help.  Hope to talk to ya again up here sometime.
Rick

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by:scraig84
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Glad to hear you got it going!
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